Chronic kidney disease (CKD) is an important health problem in the elderly, with an increasing incidence of kidney failure and a high prevalence of earlier stages of CKD, with poor outcomes and high cost. It is well known that GFR declines and albuminuria increases with aging, and that both are associated, independently and in combination, with an increased risk for kidney failure, complications of CKD and cardiovascular disease (CVD). However, the causes of age-related changes in kidney function are not well understood, in large part, due to absence of reliable information about the level of GFR in a representative elderly population. Our central hypothesis is that decreased GFR and increased albuminuria in the elderly reflect microvascular disease in the kidney due to exposure to CVD risk factors throughout the life course, mediated in part by increased aortic stiffness. The Age, Gene/Environment Susceptibility-Reykjavic Study (AGES-Reykjavik Study) (N01-AG-1-2100) is a genetic epidemiology study nested in a population based cohort study of CVD in Iceland begun in 1967. Iceland has a burden of CVD similar to the US Caucasian population. The study includes a comprehensive assessment of CVD risk factors in mid-life;vascular, neurocognitive, musckoskeletal and metabolic phenotypes of quantitative traits in late life;and a genome wide scan. We propose an ancillary study to the current visit. Specific aims include: 1. To determine the level of measured GFR by age, sex and CVD risk factors. We will measure GFR using plasma clearance of iohexol in a subcohort (N=800). 2. To determine the burden of CKD in aging. We will assay creatinine, cystatin C and albuminuria in all subjects (N=3484), relate them to CKD complications, clinical and subclinical CVD and CVD risk factors and compare the results to a comparable US population (NHANES 99-04). 3. To relate late-life kidney function to midlife and late-life CVD risk factors and late-life aortic stiffness. Measures of aortic stiffness were obtained in 940 subjects at the previous visit and will be obtained in all subjects at the current visit (N=3484). Measurement of GFR and aortic stiffness in a representative cohort of community dwelling elderly individuals will allow the most accurate investigation of the level of kidney function, burden of CKD, and potential mechanisms for the decline in kidney function with age. This information is essential for the identification of modifiable risk factors for development of CKD, as well as development of targeted strategies for prevention and treatment of CKD in the elderly. The principal investigator and research team are ideally suited to carry out this investigation. Their expertise, together with the unique design and comprehensive assessment in the AGES-Reykjavik Study, will allow for the most comprehensive and rigorous examination of relationships among kidney function, aortic stiffness and aging. Project Narrative: Chronic kidney disease is a common problem in the elderly that is associated with an increased risk for kidney failure, complications of low kidney function and disease of the heart and blood vessels. Kidney function goes down with age but the cause is not completely understood and is thought to be related to high blood pressure caused by stiffening of the aorta that occurs with aging. This study will measure kidney function and stiffening of the aorta in a group of community dwelling older adults.